During the last decade, the cost of housing in the United States, and in some of the other industrialized countries of the world, has risen tremendously. In the United States in particular interest rates which were unheard of, and illegal, ten years ago are now commonplace. The 1970s saw interest rates in excess of 20% on mortgage money. This has led to a situation in which many middle class people have been unable to purchase single family dwellings.
Partly in response to this situation, lower cost methods of construction of housing have been developed. A number of prefabricated housing units are available in the market and have become quite popular in recent years due to the increase in quality of such units and their relatively low cost. Such units often include a number of standardized components which may be used in more than one particular house of the manufacturer, thus reducing the manufacturer's cost of inventory, and the need to employ skilled labor to fabricate custom components for a house.
As anyone who has ever attempted it knows, the construction of staircases in the conventional manner requires a fair degree of skill and precision measuring and cutting. In the conventional manner, a pair of parallel boards are disposed between a lower surface and an upper surface, normally first and second floors, to form a pair of stringers. When the location and length of the stringers are determined, perpendicular rectilinear cuts are made on the stringers at regular intervals. The horizontal portions of these cuts support the treads and the risers are attached to the vertical portions of the cuts during normal stair construction.
It is most desirable in constructing a staircase to make sure that stairs are regularly spaced and that the distance between the top stair and the second floor and the bottom stair and the first floor be commensurate with the distance between treads on the balance of the staircase. This is important for both aesthetic and safety reasons. Since people often walk down stairs at night, without the aid of light, or early in the morning when they are not fully awake, a discontinuity in the distance between adjacent treads, or a tread and a floor surface can give rise to an unpleasant surprise and often injury to the ankle or knee of a person who encounters such a discontinuity and is not prepared for it.
Many makers of prefabricated houses have adopted standard staircases as components of such housing and thus a large number of stringers wih the same cuts can be fabricated by the manufacturer and used in a variety of different units. However, the prior art has not provided an inexpensive and efficient apparatus which may be used to construct stairs between floors separated by a variety of distances which will still provide the desirable even spacing between adjacent treads, the top and bottom treads, and the floor surfaces.
Several prior art arrangements for providing prefabricated metal stairs have been made. For example, the method described in U.S. Pat. No. 3,839,840 shows an arrangement for constructing metal stairs where the stringers are provided with the flanges of a conventional "I-beam". A prefabricated cason for use in constructing metal staircases is also shown in British Pat. No. 1,082,462.
However, neither of these arrangements are satisfactory, or applicable to the more commonly encountered situation of constructing staircases in homes and other buildings in which wooden stringers are normally used.